1. Technical Field
This disclosure relates generally to an image forming apparatus employing an inkjet system such as a printer, a copier, and a facsimile machine.
2. Description of the Background Art
An image forming apparatus employing an inkjet system uses a recording head including a liquid ejection head that ejects droplets of a recording liquid such as ink onto a recording medium to form images on the recording medium. In order to reliably eject ink droplets from the recording head moving reciprocally back and forth to target positions on the recording medium, a distance between a nozzle surface of the recording head and a surface of the recording medium is required to be kept constant regardless of a thickness of the recording medium.
In one example of a related-art image forming apparatus, recording heads are installed on a single carriage for protection of the recording heads. A mechanism that adjusts a height of the carriage to keep constant a distance between nozzle surfaces of the recording heads and a surface of a recording medium vertically moves the carriage mounting the recording heads upward and downward together with a guide rod that movably supports the carriage in a main scanning direction. The mechanism includes two eccentric cams operated by an operation lever via a link mechanism, thereby requiring a certain amount of space for the operation lever to slide and making it difficult to make the image forming apparatus more compact. Further, adjustment of the height of the carriage is not automatically performed but must be manually operated by a user.
In another example of a related-art image forming apparatus, a holder member that holds multiple recording heads installed on a single carriage is provided. The holder member is disposed on multiple eccentric cams arranged parallel to each other within the carriage. The multiple eccentric cams are simultaneously rotated at the same angle using a gap adjustment lever so that the multiple recording heads are lifted and lowered together with the holder member. However, although the eccentric cams are coupled to each other by racks and pinions, one of the eccentric cams is rotated by the gap adjustment lever, thereby still requiring a certain amount of space for the gap adjustment lever to slide even though the gap adjustment lever is automatically rotated. Consequently, it is difficult to make the image forming apparatus more compact.
In yet another approach, an image forming apparatus includes a first carriage including recording heads that eject monochrome ink droplets and a separate second carriage including recording heads that eject color ink droplets to form both monochrome and full-color images. The second carriage is separatably dockable with the first carriage so that unnecessary waste of color ink ejected for maintenance even during monochrome image formation is prevented and the recording heads installed on the second carriage can be protected during monochrome image formation. Specifically, only the first carriage is driven during monochrome image formation so that the recording heads of the second carriage are not driven and are protected, thereby preventing unnecessary waste of the color ink. Because various types of recording media having different thickness are used in the image forming apparatus, it is necessary to adjust a gap between a surface of each of the recording media and nozzle surfaces of the recording heads respectively mounted on the first and second carriages based on the thickness of the recording media in order to keep the gap constant. However, a technique for adjusting the gap is not disclosed for the image forming apparatus.
There is also known a technique relating to engagement and disengagement of a coupling member of a toner cartridge and a driving part of an image forming apparatus. The toner cartridge includes a developer conveyance member that rotates on a rotary shaft thereof. A drive transmission unit that receives a driving force from the image forming apparatus is movable in a direction parallel to the rotary shaft of the developer conveyance member. Specifically, the drive transmission unit is movable between a first position where the drive transmission unit receives the driving force from the image forming apparatus and a second position where the drive transmission unit is isolated from the driving force from the image forming apparatus. Accordingly, the toner cartridge is more easily attached to and detached from the image forming apparatus. However, the above-described technique is related neither to lifting and lowering the carriages to adjust the gap between the nozzle surfaces of the recording heads and the surfaces of the recording media nor docking and separation of the first and second carriages.
As described above, docking and separation of the first and second carriages performed depending on colors used for image formation and lifting and lowering the recording heads respectively installed on the first and second carriages based on the thickness of the recording media are disclosed as two separate techniques unassociated with each other in the related-art image forming apparatuses employing the inkjet system. Further, a technique that lifts and lowers the recording heads using a single drive source other than human power, such as a motor, is not yet disclosed. Meanwhile, there is increasing demand for making the configuration of the image forming apparatuses simpler and more compact.